Fuel system and process for its production for environmental protective energetic use of urban sewage sludge

ABSTRACT

The present invention relates to a fuel system and to a process for the production of such a fuel system by using urban sewage sludge. Environment protective energetic use of urban sewage sludge and the reduction of fossil Carbon dioxide are the important goals. The fuel system according to the present invention shows a content of fossil carbon which is clearly reduced compared to that of fossil fuels while the fuel-technological properties are the same. Thus the emission of the carbon dioxide based on fossil carbon is notably reduced during the use of the fuel system according to the invention. In one embodiment of the process according to the invention, the fuel system according to the invention is provided consisting of different fossil regular fuels and urban sewage sludge as biogenic carbon donor, with biomasses serving as a biogenic carbon donor.

The present invention relates to a fuel system and to a process for theenvironmental protective energetic use of urban sewage sludge.

Fuels generally serve as an energy carrier in the production of heat orelectric current. From prior art, a number of different fuels are knownamong which the so-called fossil fuels predominate.

Hard coal, brown coal, lignite, turf, natural gas and petroleum are partof the fossil fuels.

Fossil fuels have been exploited already since the 18^(th) and 19^(th)centuries, and they were considered as the basis for the IndustrialRevolution. Particularly during the past 40 years, the worldwide energydemand and hence the consumption of fossil fuels have increased to suchan extent that the production of energy from fossil fuels has causedenvironmental problems.

Fossil fuels are generally based on organic carbon compounds whichrelease energy in the form of heat during the oxidative conversion withoxygen, as this takes place during combustion. Carbon dioxide and wateris generated as a byproduct of this oxidative conversion.

Since carbon dioxide which is released during the combustion of fossilfuels originates from carbon compounds that have been stored overmillions of years, this massive combustion results in the enrichment ofthe earth's atmosphere with carbon dioxide.

On the other hand, this carbon dioxide is frequently referred to as aso-called “greenhouse gas” which could contribute to disturbing theecological balance on the earth. Carbon dioxide in the atmosphere issuspected to reduce the radiation of heat energy from the earth to theuniverse just as the glass roof of a greenhouse while the incidence ofthe sun's radiation on the earth is reduced only little. This effect issuspected to lead to global warming.

For controlling the emission of CO₂ to the atmosphere,climate-protection goals have been fixed by the European Union inconsideration of the Kyoto Protocol, and in this connection there haveeven been introduced so-called Emission Certificates. Since 2005, the EUmembership states are obliged by the EU Emissions Trading Directive tohand in a National Allocation Plan each time at the beginning of anemissions trading period. This plan fixes an amount of greenhouse gaseseach bigger emitter of a country is allowed to emit within a particularperiod. Article 9 of these Directives provides the examination andapproval of this Allocation Plan by the EU Commission on the basis of 12criteria. This concerns above all the compatibility of a country's owngoals within the scope of the Kyoto Protocol, equal treatment ofenterprises and the observance of the EU competitive law. If a company'semission exceeds the allowance that has been allocated to it, thecompany has to buy additional emission rights from another company. Thiscan be done for instance at the Energy Exchange EXXA. On the other hand,if a company emits less than the allowance that has been allocated tothis company, it may sell excess amounts of emission to other companies.However, for in fact reducing the fraction of CO₂ in the atmosphere, theallowed emissions are reduced step by step.

Major emitters of CO₂ are branches in industry and economy having a highenergy demand. These are for instance power plants, petroleumrefineries, coking plants, iron and steel works, the cement industry,glass industry, lime industry, brick industry, insulation materialindustry, ceramic industry, and cellulose and paper industry.

One way for avoiding the accumulation of CO₂ in the atmosphere is theuse of the so-called regenerative energy. In general, these are windpower, water power, solar power, and the use of biomasses as a fuel orfor the production of bio gas. However, if biomasses are used as anenergy carrier, the problem exists that these biomasses have a clearlylower energy content compared to fossil fuels. On the other hand,biomasses have the advantage that they are extracted as an energycarrier from the current carbon cycle. This means, that on a scale ofEarth history, carbon dioxide which is released as a result of theoxidative conversion of biomasses was generated only a short time agoand is also directly extracted again from the carbon cycle by theregrowing plants, if the biomasses are simultaneously planted again.Thus, a carbon dioxide balance is achieved and the accumulation ofcarbon dioxide in the atmosphere is avoided.

However, due to their clearly lower energy content, fuels based onbiomasses as known from prior art cannot be used up to present withsufficient efficiency in the big industry. Moreover, the use ofbiomasses as a fuel requires fuel technologies which are different fromthose employed in the combustion of fossil fuels such as black coal orlignite for instance. This means, that the release of a defined amountof energy would require the combustion of a clearly higher amount ofbiomasses than of fossil fuels on one side and that the use of biomassesas a fuel on an industrial scale would require an expensive modificationof already installed fueling systems on the other side.

Apart from their energy content, biomasses which are used as a fuel aredifferent from fossil fuels also with regard to further properties suchas ash content, volatile matters, hydrogen content and water content.But all these factors play an important part in the industrial use offuels in dependence of the respective application, so that frequently itis not possible to exchange fossil fuels for biomasses as a fuel in thefield of industrial applications.

U.S. Pat. No. 5,797,972 disclose a method for the production of pelletsor briquettes from sewage sludge solids. Mechanically stable pellets orbriquettes result from combining a major portion of sewage sludge solidswith lesser amount of lime and binder materials suitable for impartingstability to the product and pressing or extruding the combinedcomponents into desired shapes. Coal may be included in the pellet orbriquette composition to improve fuel value.

US 2004/0232085 A1 disclose a method for dewatering sewage sludge byusing sludge-coal-oil co-agglomeration (“SOCA”) which comprises thesteps of physically, chemically or biologically conditioning sludge toimpart hydrophobicity and lipophilicity to the sludge (conditioningstep), supplying oil and coal to the conditioned sludge with stirring toform sludge-coal-oil agglomerates (agglomerating step), enlarging theparticle diameter of sludge-coal-oil agglomerates (size enlargementstep), and remaining the enlarged sludge-coal-oil agglomerates over asieve to selectively separate them from hydrophilic materials dispersedin tailing water(screening step).

However, mixing of the sewage sludge with e.g. coal as already performedin the prior art is based on the flue value of the resulting product,only. Other combustion properties of the resulting product, likehomogeneity of the combustion and exchangeability of the product withconventional fuels have not been considered, yet.

The invention is therefore based on the object of providing a fuel whichis ecologically more favorable on one side and which can be unlimitedlyexploited for industrial applications on the other side. It is also anobject of the present invention to provide a process for the productionof such a fuel.

Concerning the fuel, this object is achieved by a fuel system accordingto claim 1. Embodiments of the inventive fuel system are considered inthe dependent claims and the embodiments as disclosed in the followingdescription.

The present teachings may solve one or more of the above-mentionedproblems and/or achieve one or more of the above-mentioned desirablefeatures. Other features and/or advantages may become apparent from thedescription which follows.

At least some of the objects and advantages of the present teachings maybe realized and attained by means of the elements and combinationsparticularly pointed out in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed. It should beunderstood that the invention, in its broadest sense, could be practicedwithout having one or more features of these exemplary aspects andembodiments.

The present teachings contemplate fuel systems and processes for theproduction of fuel systems, wherein the content of fossil carbon isreduced compared to that of fossil fuels, while the fuel-technologicalproperties are the same.

The fuel systems and processes for the production of fuel systems inaccordance with the present teachings consider a mixture of variousfossil regular fuels and urban sewage sludge as biogenic carbon donors.As those of ordinary skill in the art would understand, as used herein,the term “biogenic carbon donor” generally refers to biomasses.

Accordingly, a fuels system is provided which is characterized in thatit consists of a mixture of at least two different fossil regular fuelsand urban sewage sludge as a biogenic carbon donor, wherein the amountof the urban sewage sludge is at least 10% with respect to the totalweight.

According to the invention, urban sewage sludge is used as a biogeniccarbon donor. In the meaning of the invention urban sewage sludge refersto the residual, semi-solid material left from urban wastewater orsewage treatment processes.

In a preferred embodiment according to the invention, the urban sewagesludge used as biogenic carbon donor is the product anaerobic digestionof raw sludge, for example in so called Imhoff tanks, also referred toas biosolids.

In another preferred embodiment according to the invention, the sewagesludge is raw sludge coming from the sedimentation tank or settling tankof urban sewage plants.

Fossil regular fuels which are preferably used in the fuel systemaccording to the invention are brown coal, black coal, and anthracite.Examples of such usable coals are hard coal, fat coal, gas coal,long-flame coal, bituminous coal, pre-dried black lignite or pre-drieddull brown coal.

In a preferred embodiment of the inventive fuel system, the first fossilregular fuel has a Vitrinite reflection Rm of >2.0, whereat the secondregular fuel has a Vitrinite reflection Rm between of 0.4 to 2.0.

The Vitrinite reflection Rm gives information about the maturity and thecalorification of the fossil regular fuel used. Furthermore, theVitrinite reflection is associated with the combustion behavior of thedeployed fossil regular fuel so that an optimization of the combustionbehavior of the fuel system is possible by choosing fossil regular fuelshaving a Vitrinite reflection parameter within the specified range.Thereby, the combustion behavior of the inventive fuel system can beadapted to the combustion behavior of pure fossil fuels, like they aretypically used in e.g. power plants, whereat as combustion behavior inparticular the fuel value, the calorific value, as well as the ashresidue should be understood. This enables the use of the inventive fuelsystem in existing firing systems without further plant specificmodification. Hence, the inventive fuel system enables an ecologicaloptimization of the firing systems without the need to make plantspecific modifications.

According to a further embodiment of the inventive fuel system, at leastthree fossil regular fuels are used, whereat one having a Vitrinitereflection Rm >3.0, a second having a Vitrinite reflection Rm within therange of >2.0 and 3.0, and the third has a Vitrinite reflection Rmwithin the range of 0.4 and 2.0.

This further embodiment of the inventive fuel system enables inparticular an adaption of the hardgrove index, so that the fuel systemcan be adapted with respect to this parameter to the plant specificconditions, like e.g. coal mills, too.

In a further embodiment of the inventive fuel system, the fuel systemcomprises beside the fossil fuel and the biogenic carbon carrier arefining product of the group consisting of coke, petrol coke, lignitecoke, and charcoal.

According to another preferred embodiment of the invention, beneath thepetrographical determination of the Vitrinite reflection also thecomposition of the maceral, including the composition of the sub-maceralis taken into consideration for calculating an optimized mixture ofsewage sludge with a fossil fuel. For doing so, inert and reactivemacerales are put into an optimized relation by mixing. As a result ofthese mixtures, the sedimentation of the activated sewage sludge isoptimized. Activated sludge is a process for treating sewage treatingusing air and a biological floc composed of bacteria and protozoans. Thefossil fuel mixture, e.g. coal mixture, which is optimized with respectto its maceral and sub-maceral composition, can advantageously be usedas to improve the sedimentation of the sewage flocs in such processes insewage treatment plants.

According to another embodiment, as reactive maceral a mixture ofVitrinite, Exinite, Resinite, and ⅓ Semifusinite, whereas as inertmaceral a mixture of ⅔ Semifusinite, Micrinite, Fusinite, and mineralmaterial is used.

Vitrinite macerals are derived from the cell wall material (woodytissue) of plants, which are chemically composed of the polymers,cellulose and lignin.

Exinite (also known as Liptinite) macerals are considered to be producedfrom decayed leaf matter, spores, pollen and algal matter. Resins andplant waxes can also be part of Exinite macerals. Exinite macerals tendto retain their original plant form, i.e., they resemble plant fossils.These are hydrogen rich and have the highest caorific values of all coalmacerals.

Resinite macerals are ubiquitous, though minor, components in coalsbelow medium-volatile bituminous rank. They are usually absent in coalsof higher rank.

Fusinite is seen in most coals and has a charcoal-like structure.Fusinite is always the highest reflecting maceral present and isdistinguished by cell-texture. It is commonly broken into small shardsand fragments.

Semifusinite has the cell texture and general features of Fusiniteexcept that it is of lower reflectance. In fact, Semifusinite has thelargest range of reflectance of any of the various coal macerals goingfrom the upper end of the Pseudovitrinite range to Fusinite.Semifusinite is also the most abundant of the inertinite macerals.

Micrinite occurs as very fine granular particles of high reflectance. Itis commonly associated with the Liptinite macerals and sometimes givesthe appearance of actually replacing the Liptinite.

According to a particular preferred embodiment, the mixture of inert andreactive macerals is based on the Composition Balance Index in waste(CB6) similar calculated to the Composition Balance Index (CBI)according to N. Schapiro et al, in AIME Proceedings, Blast Furnace, CokeOven, and Raw Materials Conference 1961, Vol. 20, pg. 89ff, which ishereby incorporated by reference. Accordingly

${CBI}_{W} = \frac{{Total}\mspace{20mu} {inerts}\mspace{14mu} {in}\mspace{14mu} {the}\mspace{14mu} {fossil}\mspace{14mu} {fuel}}{{Optimum}\mspace{14mu} {inerts}\mspace{14mu} {in}\mspace{14mu} {the}\mspace{14mu} {fossil}\mspace{14mu} {fuel}}$

In another preferred embodiment, the Composition Balance Index (CB6) ofthe fossil regular fuel used in the inventive fuel system is in therange of about between ≧2 and ≦5, preferably between ≧2.5 and ≦4.5.Surprisingly it was found that by choosing the CBl_(W) within thatrange, an optimized agglomeration of the fossil fuel with the sewagesludge flocs in the activated sludge can be achieved. These improvedagglomeration leads to a stringer binding of the sludge flocs to thefossil fuel, which in turn on one hand reduces the time needed forsedimentation, on the other hand results in a fuel system having asignificantly improved combustion behavior due to an optimized value ofvolatile compounds.

In general, there are three different procedures to produce theinventive fuel system:

-   -   Procedure 1: The urban sewage sludge is putrefied, drained and        dried and then mixed with the at least two different fossil        regular fuels;    -   Procedure 2: The urban sewage sludge is mixed with at least two        different fossil regular fuels and then putrefied, drained and        dried;    -   Procedure 3: The urban sewage sludge is mixed with one of the at        least two different fossil regular fuels, putrefied, drained,        dried, and then mixed with at least one further fossil regular        fuel.

The fuel system according to the invention provides a fuel which meetsthe requirements of fossil fuels concerning its fuel-technologicalproperties while showing a clearly lower emission of CO₂ from fossilcarbon carriers, based on the releasable energy content.

Thus, the fuels system shows an effective content of fossil carbon whichis reduced by at least 11% compared to fossil fuels, referred to thecalorific value, with the percentage of fossil fuels being put in arelation to the calorific value for calculating the effective content offossil carbon.

The content of the fossil carbon in the inventive fuel system can bedetermined, for example by one of the radio carbon method, also referredto as ¹⁴C-method, and the method of selective dissolution.

The ¹⁴C-method is a radiometric dating method that uses the naturallyoccurring radioisotope carbon-14 (¹⁴C) to determine the age ofcarbonaceous materials up to about 58,000 to 62,000 years. Raw, i.e.uncalibrated, radiocarbon ages are usually reported in radiocarbon years“Befor Present” (BP), “Present” being defined as 1950. The year 1950 waschosen because it was the year in which calibration curves forradiocarbon dating were first established. 1950 also predates largescale atmospheric testing of nuclear weapons, which altered the globalratio of carbon-14 to carbon-12, the naturally most frequently occurringcarbon isotope.

When plants fix atmospheric carbon dioxide (CO₂) into organic materialduring photosynthesis they incorporate a quantity of ¹⁴C thatapproximately matches the level of this isotope in the atmosphere. Afterplants die or they are consumed by other organisms for example, byanimals, the ¹⁴C fraction of this organic material declines at a fixedexponential rate due to the radioactive decay of ¹⁴C. Comparing theremaining ¹⁴C fraction of a sample to that expected from atmospheric ¹⁴Callows the age of the sample to be estimated. Since coal, like otherfossil fuels, is the product of carbonization of plants in formergeological eras, the ¹⁴C-content of fossil and biogenic carbon sourcessignificantly differs, thereby allowing to discern between both.

When using the method of selective dissolution the probe to be examinedon its biogenic carbon content is subsequently treated with sulfuricacid and hydrogen peroxide. While the biogenic carbon is soluble in theat least one of the mentioned solvents, fossil carbon is not. As aresult the probe is depleted from biogenic carbon. Accordingly bydetermination and comparison of the total carbon content of the fossilfuel prior and after depletion, the amount of biogenic carbon can bedetermined. The determination of the total carbon content may beperformed, e.g. by determination of the ash content. Also this methodallows to discern between carbon coming from fossil and biogenic carbonsources.

Concerning the process, the object of the invention is achieved by aprocess for producing a fuel system of the above-described kind,comprising the steps of:

-   -   1. selecting a first fossil regular fuel having a low content of        volatile matters, and a Vitrinite reflection Rm >2.0, a second        fossil regular fuel having a medium content of volatile matters,        and a Vitrinite reflection Rm between 0.4 and 2.0;    -   2. mixing the first fossil regular fuel with the second fossil        regular fuel;    -   3. mixing the mixture obtained in step 2 with the sewage sludge;        wherein in Step 3 at least 10% by weight, with respect to the        total mass of the fuel system, of the sewage sludge is admixed        to the mixture obtained in step 2; or    -   1. selecting a first fossil regular fuel having a low content of        volatile matters, and a Vitrinite reflection Rm >2.0, a second        fossil regular fuel having a medium content of volatile matters,        and a Vitrinite reflection Rm between 0.4 and 2.0;    -   2. mixing one of the selected fossil regular fuel with the        sewage sludge;    -   3. mixing the mixture obtained in step 2 with the other selected        fossil regular fuel,        wherein in Step 2 at least 10% by weight, with respect to the        total mass of the fuel system, of the sewage sludge is admixed        with one of the selected fossil regular fuel.

The selected fossil regular fuel can be admixed to the sewage sludgeprior or past putrefying, draining, and drying of the sewage sludge.This means, the fossil regular fuel according to the inventive methodmay be added to the sewage sludge, for example in the settling tank,sedimentation tank, or the vessel the anaerobic digestion takes place(e.g. an Imhoff tank). When admixing at least one of the selected fossilregular fuel to the sewage sludge prior to putrefying, draining, anddrying the sludge, the regular fossil fuel beneficial can act as afiltration additive improving the draining of the sludge.

According to another embodiment of the inventive process, the fossilregular fuels are selected to provide a CBl_(W) of the fossil regularfuel mixture within a range of between ≧2 and ≦5, preferably between≦2.5 and ≧4.5.

The mixture obtained by the inventive method may be mixed further withregular fuels. Suitable regular fuels are, for example coke, petrolcoke, lignite coke, and charcoal.

The fuel system according to the invention which has been obtained by aprocess according to the invention is particularly suitable for powerplant fuelling in electric power and heat production, for paperproduction, for the production of glass and mineral melts, and thecement production.

The fuel system according to the invention and the process for itsproduction are described in the following by way of examples which arenot in any way limiting to the invention.

In the following table 1, examples of the main characteristics ofdifferent fossil fuels and biogenic carbon carriers are shown.

EXAMPLE 1

TABLE 1 Mixture Mixture Mixture Mixture A/B/C in % A/B/C in % A/B/C in %A/B/C in % urban by weight by weight by weight by weight Coal A Coal Bsludge C 33/33/33 40/30/30 50/20/30 70/20/10 Rm Vitrinite refection 2.81.2 parameters (raw, ar) water % 5.00 9.01 25.91 13.31 12.48 12.08 7.89ash % 7.60 20.50 27.03 18.38 17.30 16.01 12.12 volatile matters % 5.7021.26 43.47 23.48 21.70 20.14 12.59 sulfur % 0.80 0.93 0.12 0.62 0.640.62 0.76 hydrogen % 2.48 3.05 3.31 2.95 2.90 2.84 2.68 carbon total %78.85 57.85 23.92 53.54 56.07 58.17 69.16 ncv J/g 29.708 21.833 5.92219.154 20.210 20.997 25.754 ncv cal/g 7.096 5.215 1.414 4.575 4.8275.015 6.151 Cfoss % 78.85 57.85 4.48 47.71 50.24 52.34 67.21 Cbiogen %0.00 0.00 19.44 5.83 5.83 5.83 1.94 ar = as received, ncv = netcalorific value

A mixture auf coal A and coal B was mixed with urban sewage sludge dryin the ratios mentioned in table 1 according to procedure 1(i.e. theurban sewage sludge is putrefied, drained and dried and then mixed withthe at least two different fossil regular fuels) in a mixing drum, untila homogeneous mixture was obtained. In the analytical examination theobtained mixture showed a water content, an ash content, a volatilematerial fraction, a sulfur content, and a total carbon content asmentioned in table 1. The biogenic carbon concentration was in the rangeof between 1.94 and 5.83% by weight of the total mass. Accordingly, thefuels system shows an effective content of fossil carbon which isreduced by at least 1.94% to about 6% absolute compared to fossil fuels,referred to the calorific value, with the percentage of fossil fuelsbeing put in a relation to the calorific value for calculating theeffective content of fossil carbon. The obtained mixture showed a ncv Huof 4785 cal/g.

The obtained mixture showed an excellent combustion behavior and couldbe combusted in a stoker-fired furnace previously operated with fossilfuels, without any modification of the installation.

EXAMPLE 2

TABLE 2 Mixture Mixture Mixture Mixture A/B/C in % A/B/C in % A/B/C in %A/B/C in % urban by weight by weight by weight by weight Coal A Coal Bsludge C 33/33/33 40/30/30 50/20/30 70/20/10 Rm Vitrinite refection 2.81.2 parameters (raw, ar) water % 5.00 9.01 10.00 8.00 7.70 7.30 6.30 ash% 7.60 20.50 23.74 17.28 16.31 15.02 11.79 volatile matters % 5.70 21.2652.81 26.59 24.50 22.95 13.52 sulfur % 0.80 0.93 0.15 0.63 0.64 0.630.76 hydrogen % 2.48 3.05 4.02 3.18 3.11 3.06 2.75 carbon total % 78.8557.85 38.16 58.29 60.34 62.44 70.58 ncv J/g 29.708 21.833 9.992 20.51121.431 22.218 26.161 ncv cal/g 7.096 5.215 2.387 4.899 5.119 5.307 6.249Cfoss % 78.85 57.85 20.60 53.02 55.08 57.18 68.83 Cbiogen % 0.00 0.0017.56 5.27 5.27 5.27 1.76 ar = as received, ncv = net calorific value,

A mixture auf coal A and coal B was mixed with urban sewage sludge dryin the ratios mentioned in table 2 according to procedure 2 (i.e. theurban sewage sludge is mixed with at least two different fossil regularfuels and then putrefied, drained and dried) in a mud basin, until ahomogeneous mixture was obtained. The mixture takes place in an urbansewage plant. In the mud basin the sewage sludge is mixed with a mixtureof coal A and coal B by simply adding the coal mixture to the mud basinand using the basins agitator to obtain a homogeneous mixture.Afterwards the mixture is drained by reducing of water. The admixing ofthe coal to the raw sewage sludge improves the necessary drainage of thesewage sludge.

In the analytical examination the obtained mixture showed a watercontent, an ash content, a volatile material fraction, a sulfur content,and a total carbon content as mentioned in table 2. The biogenic carbonconcentration was in the range of between 1.76 and 5.27% by weight ofthe total mass. Accordingly, the fuels system shows an effective contentof fossil carbon which is reduced by at least 1.76 to about 6% absolutecompared to fossil fuels, referred to the calorific value, with thepercentage of fossil fuels being put in a relation to the calorificvalue for calculating the effective content of fossil carbon. Theobtained mixture showed a ncv Hu of 4522 cal/g.

The obtained mixture showed an excellent combustion behavior and couldbe combusted in a stoker-fired furnace previously operated with fossilfuels, without any modification of the installation.

Accordingly, the present invention contemplate fuel systems andprocesses for the production of fuel systems, wherein the content offossil carbon is reduced compared to that of fossil fuels, while thefuel-technological properties are the same.

The present invention can be understood from the following detaileddescription either alone or together with the accompanying drawings. Thedrawings are included to provide a further understanding of the presentteachings, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiments of thepresent teachings and together with the description serve to explain theprinciples and operation.

FIG. 1 is a process flow diagram illustrating the production of a fuelsystem in accordance with the present teachings;

FIG. 2 is a flow diagram illustrating a first procedure for producing afuel system in accordance with the present teachings;

FIG. 3 is a flow diagram illustrating a second procedure for producing afuel system; and

FIG. 4 is a flow diagram illustrating a third procedure for producing afuel system.

As illustrated in FIG. 1, the fuel systems and processes for theproduction of fuel systems in accordance with the present teachingsconsider a mixture of various fossil regular fuels and urban sewage,wherein the urban sewage sludge act as biogenic carbon donors. As thoseof ordinary skill in the art would understand, the mean random Vitrinitereflectance Rm gives information about the maturity and thecalorification of a fossil regular fuel and the macerals comprised. TheRm is further associated, for example, with the combustion behavior of afossil regular fuel. Accordingly, the combustion behavior of the fuelsystem may be optimized and adapted to the combustion behavior of purefossil fuels (e.g., typically used in power plants) by choosing fossilregular fuels having a mean random Vitrinite reflectance parameterwithin a specified range, especially with respect to the maceralcomposition. In other words, the fuel technological properties of thefuel system (e.g., the fuel value, the calorific value, and the ashresidue) may be adapted to the fuel technological properties of purefossil fuels. This may, for example, enable fuel systems of the presentteachings to be used in existing combustion systems without furtherplant-specific modification as shown in FIG. 1.

The fuel systems of the present invention may be produced using variousprocesses. In various exemplary embodiments, for example, using a firstprocedure (i.e., Procedure 1) as shown in FIG. 2, urban sewage sludgecan be putrefied, drained and dried and then mixed with at least twofossil regular fuels.

In various additional exemplary embodiments, using a second procedure(i.e., Procedure 2) as shown in FIG. 3, urban sewage sludge can be mixedwith at least two fossil regular fuels and then putrefied, drained anddried.

In various further exemplary embodiments, using a third procedure (i.e.,Procedure 3) as shown in FIG. 4, urban sewage sludge can be mixed with afirst fossil regular fuel, putrefied, drained and dried, and then mixedwith at least a second fossil regular fuel.

In various exemplary embodiments of the present invention, the fuelsystems provide a fuel which meets the requirements of fossil fuels(i.e., requirements concerning fossil fuel fuel-technologicalproperties), while showing substantially lower emissions of CO₂ fromfossil carbon carriers, based on the releasable energy content. Invarious embodiments, for example, the biogenic carbon carrier fractionin the fuel system is at least about 10% by weight, referred to as thetotal mass. In various embodiments of the present invention, forexample, the fuel systems and processes for the production of fuelsystems consider a mixture of at least two differing fossil regularfuels and urban sewage sludge as a biogenic carbon donor, wherein theamount of the urban sewage sludge is at least about 10% with respect toa total weight of the mixture.

In various exemplary embodiments, for example, a first fossil regularfuel may have a mean random Vitrinite reflectance Rm of greater thanabout 2.0, and a second fossil regular fuel may have a mean randomVitrinite reflectance Rm ranging from about 0.4 to about 2.0.

1-12. (canceled)
 13. A fuel system comprising: a fuel mixture comprisingat least two different fossil regular fuels; and urban sewage sludge asa biogenic carbon donor, wherein the urban sewage sludge comprises atleast about 10% by weight of a total mass of the fuel system.
 14. Thefuel system of claim 13, wherein the at least two fossil regular fuelsare chosen from brown coal, black coal, anthracite, and combinationsthereof.
 15. The fuel system of claim 13, wherein a first fossil regularfuel has a mean random vitrinite reflectance of greater than 2.0, and asecond fossil regular fuel has a mean random vitrinite reflectanceranging from 0.4 to 2.0.
 16. The fuel system of claim 13, wherein thefuel system comprises at least three different fossil regular fuels. 17.The fuel system of claim 16, wherein a first fossil regular fuel has amean random vitrinite reflectance of greater than 3.0, a second fossilregular fuel has a mean random vitrinite reflectance ranging from 2.0 to3.0, and a third fossil regular fuel has a mean random vitrinitereflectance ranging from 0.4 to 2.0.
 18. The fuel system of claim 13,wherein a composition balance index of each of the fossil regular fuelsranges from 2.0 to 5.0.
 19. The fuel system of claim 13, wherein acomposition balance index of each of the fossil regular fuels rangesfrom to 2.5 to 4.5.
 20. The fuel system of claim 13, wherein the urbansewage sludge is a product of anaerobic digestion of raw sludge.
 21. Thefuel system of claim 13, wherein the urban sewage sludge is raw sludgefrom a sedimentation tank and/or a settling tank of an urban sewageplant.
 22. The fuel system of claim 13, further comprising a refinementproduct chosen from coke, petroleum coke, brown coal coke, and charcoal.23. A process for producing a fuel system, the process comprising:selecting a first fossil regular fuel having a low content of volatilematters and a mean random vitrinite reflectance of greater than 2.0;selecting a second fossil regular fuel having a medium content ofvolatile matters and a mean random vitrinite reflectance ranging from0.4 to 2.0; mixing the first fossil regular fuel and the second fossilregular fuel together to form a fossil regular fuel mixture; and mixingthe fossil regular fuel mixture with an urban sewage sludge, wherein theurban sewage sludge is at least about 10% by weight of a total mass ofthe fuel system.
 24. The process of claim 23, wherein the fossil regularfuel mixture is mixed with the urban sewage sludge after the urbansewage sludge is putrefied, drained, and dried.
 25. The process of claim23, wherein the fossil regular fuel mixture is mixed with the urbansewage sludge before the urban sewage sludge is putrefied, drained, anddried.
 26. The process of claim 23, wherein each of the fossil regularfuels is selected to provide the fossil regular fuel mixture with acomposition balance index ranging from 2.0 to 5.0.
 27. The process ofclaim 23, wherein each of the fossil regular fuels is selected toprovide the fossil regular fuel mixture with a composition balance indexranging from 2.5 to 4.5.
 28. A process for producing a fuel system, theprocess comprising: selecting a first fossil regular fuel having a lowcontent of volatile matters and a mean random vitrinite reflectance ofgreater than 2.0; selecting a second fossil regular fuel having a mediumcontent of volatile matters and a mean random vitrinite reflectanceranging from 0.4 to 2.0; mixing one of the selected first or secondfossil regular fuels with an urban sewage sludge to obtain a fuelmixture; and mixing the other selected first or second fossil regularfuel with the fuel mixture, wherein the urban sewage sludge is at leastabout 10% by weight of a total mass of the fuel system.
 29. The processof claim 28, wherein one of the selected first or second fossil regularfuels is mixed with the urban sewage sludge after the urban sewagesludge is putrefied, drained, and dried.
 30. The process of claim 28,wherein one of the selected first or second fossil regular fuels ismixed with the urban sewage sludge before the urban sewage sludge isputrefied, drained, and dried.